1. Field of the Invention
The present invention relates to an image forming apparatus that can be embodied in relation to, for example, a light emitting diode (abbreviated as LED) head and a thermal head or the like.
2. Description of the Prior Art
It is known in prior art to provide a light emitting diode head comprising a plurality of blocks each having a plurality of light emitting diodes arrayed in a row, one terminal of each of the printing elements disposed at symmetric positions on adjacent blocks being connected to an individual signal line in such a manner as to arrange the individual signal line in a zigzag form, the other terminal of each of the light emitting diodes being connected to a common signal line provided for each block, thus forming a so-called dynamic drive matrix wiring pattern. At one end of the array of the blocks is disposed a driving means which sequentially selects the common signal lines in the sequence of blocks and sequentially supplies power to the light emitting diodes contained in the selected block via the individual signal lines. The driving means drives the light emitting diodes selectively, with printing data to be recorded and individually corresponding to the light emitting diodes being given in the arrayed direction of the light emitting diodes from one end to the other end of the block.
According to the above prior art, only one driving means is provided and the construction is such that the driving means drives the light emitting diodes contained in the blocks by sequentially selecting the blocks. Therefore, as the number of blocks increases, it becomes more difficult to increase the printing speed. Suppose, for example, that it takes at least 34 .mu.sec light emitting time for each energized light emitting diode to expose a photosensitized material. In this case, when a 300 dpi light emitting diode head for printing on a Japan Industrial Standard A4 paper is provided with a total of 40 blocks each having 64 light emitting diodes which are designed to be energized simultaneously, the time needed is 1.36 msec per line (=34 .mu.sec.times.40). It is therefore hoped to increase the printing speed.